ON THE STRENGTH OF LOCOMOTIVE BOILERS. 55 



As much stress has been laid upon the weakness of the stays which unites 

 the Bat surface of the boiler to the sides of the fire-box, the following ex- 

 periments clearly indicate that the fire-box stays are not the weakest parts 

 of a locomotive boiler, and that we have more to fear from the top of the 

 furnace, which under severe pressure is almost invariably the first to give 

 way. Great care should therefore be observed in the construction of this 

 part, as the cross-beams should not only be strong, but the bolts by which 

 the crown of the fire-box is suspended should also be of equal strength, in 

 order that no discrepancy should exist, and that all the parts should be pro- 

 poi'tioned to a resisting force of at least 500 lbs. on the square inch. 



Finding our knowledge with regard to the power of resistance of locomo- 

 tive boilers to strain exceedingly imperfect, I availed myself of the present 

 opportunity to determine by actual experiment the laws on which these 

 powers are founded ; and for this purpose the Directors of the London and 

 North- Western Railway Company placed in my hands an engine of the 

 same age, constructed by the same makers, and in every respect a fac-simile 

 of that which exploded. This engine was subjected to hydraulic pressure 

 as follows: — 



Experiment made May i^th, 1853, (o determine the Resisting Powers of the 

 Fire-box and Exterior Shell of No. 2 Engine on the Eastern Division of 

 the London and North Western Railway. 



In this experimenti the boiler was furnished with a valve, A, of exactly 

 1 inch area, and a lever of the annexed dimensions, as per sketch, fig. 3. This 



Fig. 3. A 



lever, 15 : 1, gave as the weight upon the valve 35 lbs., and having suspended 

 the scale, which indicated with the lever 50 lbs., the following results were 

 obtained : — 



